The present invention is related to an improved method of forming an electrolytic capacitor and an electronic capacitor formed thereby. More specifically, the present invention is related to a hybrid capacitor with improved reliability.
Hybrid capacitors are a combination of solid electrolyte technology and wet electrolytic technology. Polymer hybrid capacitors use a combination of a liquid and conductive polymer to serve as the electrolyte. The polymer offers high conductivity and a correspondingly low ESR. The liquid portion of the electrolyte, meanwhile, can withstand high voltages and provide higher capacitance ratings due to a large effective surface area.
Hybrid electrolytic capacitors offer several advantages over purely wet or purely solid electrolytic capacitors. Hybrid capacitors have significantly better endurance and humidity resistance than either their wet electrolyte or polymeric electrolyte counterparts. Hybrids also have significantly higher tolerance for large ripple currents. However, due to the presence of the liquid electrolyte hybrid capacitors have a limited life and poor reliability, particularly, at higher temperatures such as 150° C. and above. The limited life and poor reliability has restricted the utility of hybrid capacitors particularly since their use has been reduced to those applications which have minimal risk of high temperature excursions.
U.S. Pat. No. 7,497,879, which his incorporated herein by reference, describes a method of manufacturing a hybrid electrolytic capacitor including impregnating the separator of a pre-wound capacitor body with a dispersion containing a solvent and electrically conductive solid particles or powder. The solvent is removed by evaporation thereby forming an electrically conductive solid layer on a surface of the dielectric coating film. The electrically conductive solid layer is then impregnated with a liquid electrolyte solution.
WO 2012041506, which is incorporated herein by reference, introduces a dispersion comprising a dispersing agent and particles of an electrically conductive polymer with a particle size (d50) of 70 nm or less. After at least partial removal of the dispersing agent the electrically conductive polymer is impregnated with a liquid electrolyte comprising polyalkylene glycol, polyalkylene glycol derivative, or combinations thereof.
In spite of the efforts of those of skill in the art the reliability, and temperature stability, have only marginally improved. The liquid components of the liquid electrolyte are still susceptible to evaporation at the operating temperatures a capacitor is reasonably expected to experience during normal use or during the manufacturing and assembly process. There is still a significant desire for a hybrid capacitor, with the advantages offered thereby, which is stable at elevated temperatures. Such a hybrid capacitor is provided herein.